Lots of places will give you free code readings; I think AutoZone does it (might be wrong). Code readers are pretty cheap these days and are handy to have; they plug in under the dashboard. Some are self contained and others use your laptop and a USB cable. These are handy because they include explanations (sometimes) of what the code is.
Could be a misfire. Depending on the year and whether it\'s under warranty I\'d suggest making sure the gas cap is on tight, taking out the plugs and checking them, and checking for loose underhood connections. But it takes a while for a code to go away unless your code reader allows yo to clear codes. Warning: if you do clear codes, you can\'t get your car inspected for a while afterwards to avoid having peopel shut off their engine light in time for inspection!